I thought a second light would go off/on being powered from the original motion sensor light in my garage. The original motion sensor light works as usual, the second light is always on. Why? Thanks.

I had to read this three times to figure it out but I finally got it.

The only way for the MD to activate a second light is if it is wired off the red and white in the MD itself. If you wire it off the switch it will go on and off with the switch.
If you do do this make sure the MD has the capacity to work an additional light.